Students attend the Augustus F. Hawkins High School in Los Angeles on Dec. 15, 2014. In the Los Angeles Unified School District, the suspension rate has dropped from 8 percent in 2008 to 1.5 percent, after a districtwide push to stop removing children from class for minor disruptions.

What do Richmond County, Ga.; Visalia, Calif.; and Worcester, Mass., have in common?

All three are among the school districts showing the biggest rates of improvement regarding their school discipline practices.

A new report analyzing federal data on out-of-school suspensions found evidence of huge “discipline gaps” when it comes to suspension rates for minorities and students with disabilities. And it highlighted some districts with extremely high suspension rates – a factor that has been linked to lower achievement and lower graduation rates.

But it also found evidence that reliance on suspension and expulsion isn’t necessary: Rates varied wildly from state to state and district to district, and some districts were able to drastically improve their suspension rates in a very short time.

“There were more lower-suspending schools than schools at the higher end, which tells you we can reject the status quo,” said Daniel Losen, director of UCLA’s Center for Civil Rights Remedies and an author of the study, in a conference call with reporters Monday. “Part of the question is, are there less discriminatory alternatives, and there are. Schools and districts across the country are doing things differently. We need to find out why they’re being successful and use those examples to inform these schools that are off the charts [when it comes to high rates of suspension].”

The report breaks out federal data by elementary and secondary schools and gives comparative suspension rates for every district in the nation. Later this week, the latest 2011-12 school year data will be available on a website where visitors can find data for any district in the country and compare data between districts.

Educators and social-justice advocates have been emphasizing recently the harm in an over-reliance on punitive discipline policies that suspend students for often minor offenses. Research shows a high correlation between out-of-school suspension and involvement with the juvenile justice system, dropping out of school, and lowered achievement. And the outsize suspension and expulsion rates for minority students, English language learners, and students with disabilities have led many to refer to the "discipline gap" and talk about the "school-to-prison pipeline."

Nationally, 6.7 percent of white high-schoolers received out-of-school suspensions in the 2011-12 school year, compared with 23.2 percent of African-American high-schoolers, 10.8 percent of Latinos, and 18.1 percent of students with disabilities.

"Some people dismiss this as a marginal issue, but school discipline and how it undermines educational opportunity is central to student achievement and to student outcomes," said Janel George, senior education policy counsel at the NAACP Legal Defense and Educational Fund, on the call with reporters. "We cannot close achievement gaps if we don’t close discipline gaps."

Ms. George emphasized that most students aren't getting academic supports while they're suspended, allowing them to fall behind, and that many of the reasons students are suspended – like the dress-code violation that got 7-year-old Tiana Parker sent home from her Oklahoma school last year for her hairstyle – are for trivial, nonviolent reasons that may be rooted in racial stereotypes.

Florida, which suspended 5.1 percent of its elementary students and 19 percent of its secondary students in the 2011-12 school year, was the highest-suspending state for both elementary and secondary, according to the report. But Mr. Losen emphasizes that the most interesting data are at the district level, since even within a given state, suspension rates varied widely.

For instance, Missouri had the highest black suspension rate of any state for the elementary level (12.5 percent) and the biggest gap between the black and white suspension rates. But while four of the districts in Missouri (including St. Louis) suspended more than 1 in 5 of all their black elementary students, another 21 districts in the state suspended less than 5 percent of their black elementary students.

"It should shock our conscience and it should prompt action," said Losen of the districts with astronomically high suspension rates. But seeing the huge district-to-district disparities that exist, he says – and the large improvements made by many districts – "is a reason we should reject this status quo."

In Visalia – a district in central California that serves more than 30,000 students – suspension rates between 2009-10 and 2011-12 dropped from 41 percent to 16 percent. That drop, says Superintendent Craig Wheaton, "came out of deliberate work." Starting about eight years ago, the district began analyzing its expulsion and suspension data, and it worked with principals and teachers on alternative ways to approach discipline. The focus, Dr. Wheaton says, was on preventing behavior problems from occurring (or recurring), keeping kids connected to school, and focusing on the factors that lead to misbehavior.

The district encouraged teachers and principals to read a book on positive discipline, and in the past few years – too recently for any results to be included in this round of discipline data – it has begun implementing restorative justice practices and Positive Behavioral Interventions and Supports (PBIS), a discipline system that has gained traction in schools in recent years and that emphasizes prevention and support over punitive practices like suspension.

"We did it on our own: We didn’t jump into all of this to get this data to change," says Wheaton. "But obviously somewhere along the way, some of our initiatives started paying off.... We need to think about suspension and when it’s used and why it’s used and what is the most effective way to change the behavior."

A number of districts have made an effort in recent years to bring down their suspension rates, and that shift in mind-set can yield big results, says Losen. He cites a study in Denver, where the district made a systemic effort to change discipline practices, that found that, as suspension rates came down, achievement scores also increased for all racial groups at all grade levels.

"It dispels this myth that we have to kick out the bad kids so the good kids can learn," Losen says.

Other districts cited in the report as having big drops in suspension rate over the two-year period include Richmond County, Ga., where the secondary suspension rate dropped from 58 percent to 12 percent (though it rose slightly for Latino students); Worcester, Mass., which went from 37 percent to 16 percent for secondary students; and Henrico County, Va., where the secondary suspension rate fell from 31 to 14 percent.

While the report didn't examine the reasons behind changes, Losen says that interventions yielding good results include PBIS, restorative practices, an emphasis on social-emotional learning, and other ways that districts can shift away from a zero-tolerance mind-set to one more geared toward helping students succeed and intervening in positive ways. One of the biggest predictors for how often a school suspends students is the attitude of its principal, he adds.

At the district level, 38 percent of districts fell into what the report termed "low-suspending," meaning they had a secondary suspension rate of 10 percent or less for all major racial and ethnic groups. Twenty-four percent, meanwhile, met its "high-suspending" definition, suspending 25 percent or more of high-schoolers in any subgroup.